Currently 25 states and the District of Columbia have medical cannabis programs. On Nov. 8, Arkansas, Florida and North Dakota will vote on medical cannabis ballot initiatives, while Montana will vote on repealing limitations in its existing law.Despite claims that cannabis or its extracts relieve all sorts of maladies, the research has been sparse and the results mixed. At the moment, we just don’t know enough about cannabis or its elements to judge how effective it is as a medicine.What does the available research suggest about medical cannabis, and why do we know so little about it?